The present invention relates to a device for introducing a reducing agent into an exhaust pipe segment of an internal combustion engine, which leads to a reduction catalytic converter, having a reducing agent line discharging into the exhaust pipe.
Regulatory requirements for ever-lower emissions values have led to extensive developments in the field of catalytic converters, especially for reducing nitrogen oxides in the exhaust gases. Reduction catalytic converters have proved to be especially promising. Especially in diesel engines, however, it has been found that in regeneration phases, a reducing agent enrichment of the exhaust gas is necessary.
A device or systems for post-treating exhaust gases is disclosed for instance from European Patent Disclosure EP-A-0 381 236, in which an ammonia or a urea is metered into the exhaust gas as a reducing agent. In this known system, via an injection valve, the reducing agent is injected into a premixing chamber that discharges into the exhaust pipe that leads to the reduction catalytic converter. In this generic device for introducing a reducing agent into an exhaust pipe segment of an internal combustion engine that leads to a reduction catalytic converter, the premixing chamber forms a reducing agent line that discharges into the exhaust pipe.
Although some of the reducing agent is delivered via a control valve to a transport line which discharges in the exhaust pipe that leads to the reducing catalytic converter.
From German Patent Disclosure DE-A1 196 25 447, a device for post treatment of exhaust gases of an internal combustion engine is known, in which to enhance the mode of operation of a downstream reducing catalytic converter, fuel as a reducing agent is via a meter valve and introduced into the exhaust pipe via an evaporator device. The evaporator device is a metal sleeve, provided with a glow plug, and having a face-end flow opening by way of which the evaporated reducing agent is introduced into the stream of exhaust gas. In this system, although the evaporation of reducing agent is thermally reinforced, nevertheless this version is technically complicated and requires high energy consumption for heating and evaporating the reducing agent.
It is therefore the object of the invention to refine a device of this generic type for introducing a reducing agent into an exhaust pipe segment of the type defined at the outset, in such a way that good aerosol formation occurs over the widest possible performance graph range, so that the overall efficiency of the system is increased, or in other words lower NOx emissions are achieved.
In particular, in the device according to the invention for introducing a reducing agent into an exhaust pipe segment of an internal combustion engine, which leads to a reduction catalytic converter, and having a reducing agent line discharging into the exhaust pipe a spray head is provided having at least one spray opening and a tapering cross section, which spray head is disposed at the orifice end of the reducing agent line. Because of the at least one spray opening, the aerosol formation of the reducing agent can be improved drastically. Because the spray head has a tapering cross section, even slight quantities of reducing agent can be efficiently converted into an aerosol. This is because the tapering cross section causes the wall film that tears off when bending of the reducing agent line occurs reunited again upstream of the spray opening. Thus a continuous atomization can be attained in a controlled and controllable way.
Preferably, the cross section of the spray head tapers in accordance with a steady, smooth curve. As an example, parabolic functions or the like can be named, so that the spray head in particular forms a kind of spherical dome. Advantageously, the cross section of the spray head tapers at least partly linearly, and in particular a conelike dome is formed. In that case, the spray opening should be disposed at a location where a closed wall film exists even when the quantity of reducing agent is very slight.
To further improve the aerosol formation, the spray opening or each spray opening forms an angle with the axis of the spray head of at least 5xc2x0 and especially preferably approximately 50xc2x0. The angle of the spray opening or openings depends, among other factors, on the spray cone formed, the size of the spray openings, the volumetric throughput of the spray openings, the exhaust pipe diameter, and the volumetric flow of exhaust gas.
In a preferred embodiment, a plurality of spray openings are provided, distributed circumferentially over the spray head. For example, eight spray openings may be provided, distributed at equal intervals along the circumference, so that the individual spray cones practically form a ring of aerosol fog, which assures an especially uniform distribution of the reducing agent in the exhaust gas.
Advantageously, the number of spray openings, the disposition, the orientation and/or the cross section of the spray opening or spray openings is dependent on the type and/or quantity of the exhaust gas and on the diameter of the exhaust pipe. In particular, at a high exhaust gas speed, the reducing agent line can be acted upon, for instance by a pump, the discharge rate and the aerosol formation of the reducing agent can be improved further, especially if because of the action upon it, a marked pressure difference exists between the reducing agent line and the exhaust pipe segment.
Further advantages and characteristics of the invention will become apparent from the ensuing detailed description of a currently preferred embodiment in conjunction with the accompanying drawing.